There has been developed a microphone array device that has a plurality of sound receiving parts receiving sounds, respectively converting the sounds to sound signals and outputting the signals, such as condenser microphones, and performs a variety of sound processing based upon the sound signals outputted from the respective sound receiving parts. There are cases where the microphone array device is configured so as to perform “delay-and-sum” processing for synchronizing the respective sound signals outputted from the respective sound receiving parts and adding up the synchronization values to emphasize a target sound. Further, there are cases where the microphone array device is configured so as to perform noise suppression by synchronous subtraction processing for synchronizing the respective sound signals and subtracting the one from the other to form a blind spot with respect to a noise source (e.g., Kaneda, Yutaka, “Response of digital filters in microphone systems”, Acoustical Society of Japan, 45(2), pp. 125-128, 1989).
Noise suppressing processing and target sound emphasizing processing as microphone array processing performed by the microphone array device, such as the synchronous addition processing and the synchronous subtraction processing, certainly causes occurrence of distortion of the sound signal after execution of the processing. Especially when the microphone array processing is performed on a sound signal received in a quiet environment, a distortion that occurred due to the microphone array processing is highly visible. On the other hand, as for a sound signal received in a noisy environment, even when a certain degree of distortion occurs in the signal, suppressing noise by the microphone array processing leads to improvement in sound quality.
Accordingly, there has hitherto been used a noise suppressing device configured so as to switch whether or not to execute the microphone array processing in accordance with an ambient noise level. FIG. 11 is a block diagram illustrating an example of embodiments of the conventional noise suppressing device. The conventional noise suppressing device includes sound receiving parts 101, 102, a noise level estimating part 103, a noise suppression processing controlling part 104, switches 105, 106, 109, a noise suppression processing part 107, microphone array processing part 108, and the like.
Based upon a received sound, the sound receiving part 101 performs conversion to a sound signal as an electric signal, and sends the converted sound signal to the noise level estimating part 103 and the switch 105. Based upon a received sound, the sound receiving part 102 performs conversion to a sound signal as an electric signal, and sends the converted sound signal to the switch 106.
It is to be noted that the sound signals (analog signals) outputted from the sound receiving parts 101, 102 are amplified by an amplifier (not illustrated), converted by an analog/digital converter (hereinafter referred to as A/D converter) (not illustrated) to the digital signal, and then sent to the noise level estimating part 103 and the switches 105, 106.
The noise suppression processing part 107 acquires a sound signal outputted from one end of the switch 105, and performs the noise suppressing processing based upon the acquired sound signal. Specifically, based upon a sound signal outputted from one microphone (sound receiving part 101), the noise suppression processing part 107 performs processing for detecting a noise component included in this sound signal and removing the detected noise component from the sound signal.
The microphone array processing part 108 acquires sound signals outputted from respective one ends of the switches 105, 106, and performs microphone array processing such as the “delay-and-sum” processing or the synchronous subtraction processing, based upon the acquired sound signals. The noise level estimating part 103 estimates an ambient noise level based upon the sound signal outputted from the sound receiving part 101. Further, the noise suppression processing controlling part 104 controls the switches 105, 106, 109 based upon the noise level estimated by the noise level estimating part 103.
When the noise level estimated by the noise level estimating part 103 is equal to or greater than a given value, the noise suppression processing controlling part 104 controls switching of the switches 105, 106 so as to output the sound signals from the sound receiving parts 101, 102 to the microphone array processing part 108. Further, at this time, the noise suppression processing controlling part 104 controls switching of the switch 109 so as to output the sound signal from the microphone array processing part 108 to the outside.
Meanwhile, when the noise level estimated by the noise level estimating part 103 is smaller than the given value, the noise suppression processing controlling part 104 controls switching of the switches 105, 106 so as to output only the sound signal from the sound receiving part 101 to the noise suppression processing part 107. Further, at this time, the noise suppression processing controlling part 104 controls switching of the switch 109 so as to output the sound signal from the noise suppression processing part 107 to the outside.
With such an example of a configuration, in the case of the quiet ambient environment, the noise suppressing device is capable of performing the noise suppressing processing by the noise suppression processing part 107 by use of one microphone, and in the case of the noisy ambient environment, the noise suppressing device is capable of performing the microphone array processing by the microphone array processing part 108. Therefore, the noise suppressing device is capable of suppressing noise by the processing in accordance with an ambient environment, which leads to improvement in target sound quality.